I have a Python Elastic Beanstalk load-balanced app. Here is the path a user request takes on its way into the Elastic Beanstalk app:
user -> Elastic Beanstalk ELB -> Elastic Beanstalk mod_wsgi
The first ~2-4 requests from
eb deploy of a new app version will generate 504 errors from the ELB.
After these ~2-4 requests that generate 504s, everything is fine! 200s all around.
When the 504s happen, zero requests make it through to the
Elastic Beanstalk mod_wsgi app according to
/var/httpd/access_log. I only see the 200s after the ELB has decided to start working again.
Things I have tried that didn't work:
- I increased the
Elastic Beanstalk ELBIdle Timeout to 300 seconds
- I increased the
Elastic Beanstalk mod_wsgiapache
KeepAliveTimeoutto 300 seconds as suggested here: http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/ts-elb-error-message.html
One might say, "just live with the 504s!"
However, the actual problem is that in my production setup, I have
Elastic Beanstalk ELB. CloudFlare is set to aggressively cache
.js files, since I append md5 hashes to static file URLs. When requests for these important files fail with 504, CloudFlare appears to cache these failures as being 404s. Further requests for these files 404, thus breaking the visual styling of the site on every deploy.
Deploying the Elastic Beanstalk app again with the same app version will fix the CloudFlare 404 problem. This is not a great solution. I want to keep on using CloudFlare because it makes for an excellent transparent CDN, so getting rid of it is not a solution, either.
It's hard to believe I'm alone with this issue, but Google, stackoverflow/serverfault, and the AWS forums have not yielded any solutions—or even similar problem reports. I am hoping that my description of this behavior rings a bell with someone here. Thanks in advance.